Dyed trivalent chromium conversion coatings and methods of using same

ABSTRACT

An aqueous conversion coating solution comprises a trivalent chromium compound, a zirconate compound, and a dye compound. The trivalent chromium compound can comprise trivalent chromium compounds such as trivalent chromium sulfate. The dye compound can comprise an azo dye, a chromium complex dye, an anthraquinoid dye, and/or a methine dye. The zirconate compound can comprise alkali metal hexafluorozirconate compounds. The conversion coating solution can comprise a phosphorous compound such as an organic amino-phosphonic acid compound. The conversion coating solution can be formed by mixing a dye additive containing the dye with a trivalent chromium conversion coating solution that does not contain a dye. The conversion coating solution can be used to treat metal substrates comprising aluminum, magnesium, and/or zinc.

BACKGROUND OF CERTAIN ASPECTS OF THE DISCLOSURE

Conversion coatings are widely used to treat metal surfaces to improvecorrosion resistance, increase adhesion of subsequent coatings such aspaint, form a decorative finish, or retain electrical conductivity.Conversion coatings are formed by applying a conversion coating solutionto the metal. The conversion coating solution and the metal react toconvert or modify the metal surface into a thin film with the desiredfunctional characteristics. Conversion coatings are particularly usefulfor the surface treatment of metals such as aluminum, zinc, andmagnesium.

Conversion coatings containing hexavalent chromium have been used foryears to successfully treat a variety of metal surfaces. Despite theirsuccess, they have fallen out of favor due to the high toxicity ofhexavalent chromium. This compound significantly increases the hazardsfor process personnel and increases operating and waste disposal costs,particularly in locations where it is highly regulated and subject toburdensome use and handling restrictions. Hexavalent chromium conversioncoatings are being replaced by non-hexavalent chromium conversioncoatings such as those utilizing trivalent chromium.

Dyes can be added to convention hexavalent conversion coatings to imparta specific color to the metal surface. This may be done to make a parteasy to visually identify and/or otherwise give it a unique visualappearance. The use of dyes with naturally clear trivalent chromiumconversion coatings has enjoyed less success. There are few dyes thatare suitable for use with trivalent chromium conversion coatings.

A few trivalent chromium conversion coating solutions have beenformulated over the years with a dye. One such solution includes copperphthalocyanine as the dye and is used to coat aluminum. Another solutionincludes catechol violet as the dye and is also used to coat aluminum.Although these conversion coating solutions work to a certain extent,they suffer from a number of problems.

One problem is that they tend to produce weak and uneven color on themetal surface, which make them unsuitable from an aesthetic standpoint.Another problem is that they are incompatible with many trivalentchromium conversion solutions. The dyes can cause substantialprecipitation of the constituents in the trivalent chromium conversioncoating solution. The precipitation causes powdering of the surface ofthe metal, deactivation of the bath, reduction in coatingperformance—specifically corrosion resistance, and the need forcontinual replenishment of the dye. In some situations, the dyes canquickly render the solution completely inactive. This is especially aproblem with trivalent chromium coating solutions containing phosphates.

BRIEF SUMMARY OF SOME ASPECTS OF THE DISCLOSURE

A number of embodiments of a dye containing trivalent chromiumconversion coating solution and/or a dye additive that can be used toform such solutions are disclosed. The conversion coating solutionbroadly includes a non-hexavalent chromium compound and a dye compound.In some embodiments, it includes a trivalent chromium compound, a dyecompound, and a zirconate compound. The conversion coating solution doesnot include any or only insignificant amounts of hexavalent chromium.Methods for using the conversion coating solution to dye metalsubstrates are also disclosed.

The trivalent chromium conversion coating solution is used to form acolored protective coating on a metal substrate. The coating generallypassivates the metal surface or, in other words, makes it lesssusceptible to corrosion and/or other undesirable reactions in thefuture. The dye reacts with the metals in the coating and in the metalsubstrate to form a color that is stable and easily seen. The color canbe used for identification purposes, cosmetic purposes, and/or to otherpurposes that involve changing or adjusting the visual characteristicsof the metal substrate.

The dye containing trivalent chromium conversion coating solutionprovides a number of advantages compared to what has been done in thepast. One advantage is that the dye produces less precipitation of theconversion coating chemicals. This increases the life and overalleffectiveness of the coating bath and, consequently, increases thecorrosion resistance of the treated surfaces.

The trivalent chromium compound can be any suitable trivalent chromiumcompound. One example of a suitable trivalent chromium compound istrivalent chromium sulfate. It should be appreciated that othertrivalent chromium compounds can also be used.

A wide range of suitable dye compounds can be used in the conversioncoating solution. For example, the dye compound can include azo dyes,chromium complex dyes, anthraquinoid dyes, and/or a methine dyes. Insome embodiments, the dye compound includes metal complex azo dyes,chromium complex azo dyes, and/or metal free azo dyes.

The trivalent chromium conversion coating solution can be formed anumber of ways. In some embodiments, it is formed by mixing all of thecomponents together to form a final mixed solution that is packaged forsale and use. In some other environments, it is formed by mixing a dyeadditive that contains at least the dye with an already preparedtrivalent chromium conversion coating solution or solution concentrate.This makes it possible to add a dye to any pre-existing trivalentchromium conversion coating solution or solution concentrate. The dyeadditive can include other compounds besides the dye compound. Forexample, the dye additive can include a corrosion inhibitor compoundand/or a trivalent chromium compound.

The dye containing trivalent chromium conversion coating solution can beused to treat a variety of metal substrates. It can be used to treatmetal substrates made of a single elemental metal or various metalalloys. It can also be used to treat metal substrates that have alreadybeen subjected to a surface treatment such as anodizing, plating,stretching, and the like. The conversion coating solution is especiallysuitable for treating metal substrates that comprise aluminum,magnesium, and/or zinc. Other suitable metal substrates include thevalve metals.

A variety of methods can be used to apply the conversion coatingsolution to the metal substrate. The conversion coating solution can beapplied as an immersion bath, spray, brush application, wipeapplication, and/or the like. One method involves immersing the metalsubstrate in a bath of the conversion coating solution. Another methodinvolves spraying the conversion coating solution onto the metalsubstrate.

There are other novel aspects and features of this disclosure. They willbecome apparent as this specification proceeds. Accordingly, this briefsummary is provided to introduce a selection of concepts in a simplifiedform that are further described below in the detailed description. Thesummary and the background are not intended to identify key concepts oressential aspects of the disclosed subject matter, nor should they beused to constrict or limit the scope of the claims. For example, thescope of the claims should not be limited based on whether the recitedsubject matter includes any or all aspects noted in the summary and/oraddresses any of the issues noted in the background.

DRAWINGS

The preferred and other embodiments are disclosed in association withthe accompanying drawings in which:

FIG. 1 is a color photograph showing two magnesium substrate samplescoated as follows. The sample on the left was coated with a trivalentchromium conversion coating solution comprising a dye. The sample on theright was coated with the same conversion coating solution exceptwithout the dye.

FIG. 2 is a color photograph showing two zinc substrate samples coatedas follows. The sample on the left was coated with a trivalent chromiumconversion coating solution comprising a dye. The sample on the rightwas coated with the same conversion coating solution except without thedye.

FIG. 3 is a color photograph showing two aluminum substrate samplescoated as follows. The sample on the right was coated with a trivalentchromium conversion coating solution comprising a dye. The sample on theleft was coated with the same conversion coating solution except withoutthe dye.

DETAILED DESCRIPTION

A number of embodiments of a dyed or colorized trivalent chromiumconversion coating solution are disclosed along with additives that canbe used to form the solution and methods for treating a substrate withthe solution. In general, the trivalent chromium conversion coatingsolution includes a trivalent chromium compound, a zirconate compound,and a dye compound. The conversion coating solution can be used to dye ametal surface or part as well as improve the metal's corrosionresistance, abrasive properties, and adhesion bonding properties.

The trivalent chromium conversion coating solution may provide one ormore of the following improvements/advantages over conventionalsolutions: 1) reduced precipitation, 2) longer bath life, 3) bettercorrosion resistance of treated surfaces, 4) and/or does not deactivatesolution baths comprising a phosphorous compound.

Trivalent Chromium Compound

The trivalent chromium compound can be any suitable trivalent chromiumcompound capable of forming a conversion coating on the metal substrate.Examples of suitable trivalent chromium compounds can be found in thepatents incorporated by reference at the end of the description.

The trivalent chromium compound can be a water-soluble trivalentchromium compound such as a trivalent chromium salt. It is generallydesirable to use chromium salts that provide anions that are not ascorrosive as chlorides. Examples of such anions include nitrates,sulfates, phosphates, and acetates. In a preferred embodiment, thetrivalent chromium compound is a trivalent chromium sulfate. Examples ofsuch compounds include Cr₂(SO₄)₃, (NH₄)Cr(SO₄)₂, or KCr(SO₄)₂.

It should be appreciated that the conversion coating solution caninclude one or multiple trivalent chromium compounds. For example, inone embodiment, the conversion coating solution includes a singletrivalent chromium compound. In another embodiment, the conversioncoating solution includes two, three, four, or more trivalent chromiumcompounds.

The conversion coating solution can include any suitable quantity of thetrivalent chromium compound. Examples of suitable quantities can befound in the patents incorporated by reference at the end of thedescription. In some embodiments, the conversion coating solutionincludes approximately 0.1 g/liter (0.01 wt %) to approximately 20g/liter (2 wt %) of the trivalent chromium compound, approximately 0.2g/liter (0.02 wt %) to approximately 10 g/liter (1 wt %) of thetrivalent chromium compound, or approximately 0.5 g/liter (0.05 wt %) toapproximately 8 g/liter (0.8 wt %) of the trivalent chromium compound.

In other embodiments, the conversion coating solution includes at leastapproximately 0.1 g/liter (0.01 wt %) of the trivalent chromiumcompound, at least approximately 0.2 g/liter (0.02 wt %) of thetrivalent chromium compound, or at least approximately 0.5 g/liter (0.05wt %) of the trivalent chromium compound. In still other embodiments,the conversion coating solution includes no more than 20 g/liter (2 wt%) of the trivalent chromium compound, no more than 10 g/liter (1 wt %)of the trivalent chromium compound, or no more than 8 g/liter (0.8 wt %)of the trivalent chromium compound.

Dye Compound

The dye compound (alternatively referred to as a pigment compound orcolorant compound) can be any material that is compatible with theconversion coating solution chemistry and is capable of imparting acolor to the metal substrate. In some embodiments, the dye compoundincludes one or more metal atoms and in other embodiments it does not.In those embodiments where the dye compound includes one or more metalatoms, the metal atom can be present as part of a metal complex.

In some embodiments, the dye compound can include an azo dye, a chromiumcomplex dye, an anthraquinoid dye, and/or a methine dye. In a preferredembodiment, the dye compound includes a metal complex azo dye, achromium complex dye, and/or metal free azo dye. It should beappreciated that azo dyes include monoazo dyes, disazo dyes, and/ortrisazos dyes. Example of suitable dyes include any of those describe inthe Examples below.

Numerous other dye compounds can be used as long as they are compatiblewith the other constituents in the conversion coating solution. Examplesof such dyes include those used to anodize aluminum and colorizetextiles. Other examples include acid dyes, mordant dyes, metal-complexdyes, triphenylmethane dyes, xanthene dyes, wool dyes, silk dyes, directdyes, reactive dyes, vat dyes, and the like. It is understood that thesedyes may be classified in more than one way such as by structure or bytypical use—e.g., a dye may be referred to as a chrome dye, a mordantdye, a wool dye, etc.

It should be appreciated that the conversion coating solution caninclude one or multiple dye compounds including any quantity and/orcombination of the dyes described above. In some embodiments, thetrivalent chromium conversion coating solution comprises approximately0.1 g/liter (0.01 wt %) to approximately 20 g/liter (2 wt %) of the dyecompound, approximately 0.2 g/liter (0.02 wt %) to approximately 10g/liter (1 wt %) of the dye compound, or approximately 0.5 g/liter (0.05wt %) to approximately 5 g/liter (0.5 wt %).

In some other embodiments, the conversion coating solution comprises atleast approximately 0.1 g/liter (0.01 wt %) of the dye compound, atleast approximately 0.2 g/liter (0.02 wt %) of the dye compound, or atleast approximately 0.5 g/liter (0.05 wt %) of the dye compound. In yetother embodiments, the conversion coating solution comprises no morethan 20 g/liter (2 wt %) of the dye compound, no more than 10 g/liter (1wt %) of the dye compound, or no more than 5 g/liter (0.5 wt %) of thedye compound.

Zirconate Compound

The zirconate compound can be any suitable zirconate compound that iscapable of facilitating the formation of a protective coating on asubstrate. Examples of suitable zirconate compounds include alkali metalhexafluorozirconate compounds such as potassium hexafluorozirconate,sodium hexafluorozirconate, and fluorozirconic acid.

In some embodiments, the conversion coating solution comprisesapproximately 0.2 g/liter (0.02 wt %) to approximately 20 g/liter (2 wt%) of the zirconate compound, approximately 0.5 g/liter (0.05 wt %) toapproximately 18 g/liter (1.8 wt %) of the zirconate compound, orapproximately 1 g/liter (0.1 wt %) to approximately 15 g/liter (1.5 wt%) of the zirconate compound.

In some other embodiments, the conversion coating solution comprises atleast approximately 0.2 g/liter (0.02 wt %) of the zirconate compound,at least approximately 0.5 g/liter (0.05 wt %) of the zirconatecompound, or at least approximately 1 g/liter (0.1 wt %) of thezirconate compound. In yet other embodiments, the conversion coatingsolution comprises no more than approximately 20 g/liter (2 wt %) of thezirconate compound, no more than approximately 18.0 g/liter (1.8 wt %)of the zirconate compound, or no more than approximately 15 g/liter (1.5wt %) of the zirconate compound.

Other Compounds

The trivalent chromium conversion coating solution can include a varietyof additional compounds. Examples of additional compounds can be foundin the patents incorporated by reference at the end of the description.Any individual compound or combination of compounds disclosed in thepatents can be included in the conversion coating solution in any of thedisclosed quantities.

In some embodiments, the trivalent chromium conversion coating solutionincludes a phosphorous compound that further enhances corrosionprotection of the metal substrate. The improved corrosion protection isprovided by adsorption of phosphonate groups from an organicamino-phosphonic acid compound on a surface of the metal substrate toform a M-O—P covalent bond and subsequent formation of a networkhydrophobic layer over any active corrosion site on the metal substrate.

Examples of suitable phosphorous compounds include derivatives ofamino-phosphonic acids such as the salts and esters ofnitrilotris(methylene)triphosphonic acid (NTMP), hydroxy-,amino-alkylphosphonic acids, ethylimido(methylene)phosphonic acids,diethylaminomethylphosphonic acid, and the like. Preferably, thederivative is soluble in water. A particularly suitable phosphorouscompound for use as a corrosion inhibitor and solution stabilizer isnitrilotris(methylene)triphosphonic acid (NTMP).

The phosphorous compound can be present in the conversion coatingsolution in any suitable amount. In some embodiments, the conversioncoating solution comprises approximately 5 ppm to approximately 100 ppmof the phosphorous compound or approximately 10 ppm to approximately 30ppm of the phosphorous compound. In other embodiments, the conversioncoating solution comprises at least approximately 5 ppm of thephosphorous compound or at least approximately 10 ppm of the phosphorouscompound. In still other embodiments, the conversion coating solutioncomprises no more than approximately 100 ppm of the phosphorous compoundor no more than 30 ppm of the phosphorous compound.

The trivalent chromium conversion coating solution can also comprise afluoride compound. Examples of suitable fluoride compounds includealkali metal tetrafluoroborates (e.g., potassium tetrafluoroborate),alkali metal hexafluorosilicates (e.g., potassium hexafluorosilicate),and the like. The fluoride compound is preferably water soluble.

The fluoride compound can be present in the conversion coating solutionin any suitable amount. In some embodiments, the conversion coatingsolution comprises approximately 0.2 g/liter (0.02 wt %) toapproximately 20 g/liter (2 wt %) of the fluoride compound orapproximately 0.5 g/liter (0.05 wt %) to approximately 18 g/liter (1.8wt %) of the fluoride compound. In other embodiments, the trivalentchromium conversion coating solution comprises at least approximately0.2 g/liter (0.02 wt %) of the fluoride compound or at leastapproximately 0.5 g/liter (0.05 wt %) of the fluoride compound. In stillother embodiments, the trivalent chromium conversion coating solutioncomprises no more than 20 g/liter (2 wt %) of the fluoride compound orno more than 18 g/liter (1.8 wt %) of the fluoride compound.

In some embodiments, the trivalent chromium conversion coating solutionincludes a corrosion inhibitor additive that increases the corrosionresistance provided by the coating. Examples of suitable corrosioninhibitor compounds include any of those disclosed in CN 102888138.Other examples include 2-mercaptobenzothiazole (MBT),2-mercaptobenzimidazole (MBI), 2-mercaptobenzoxazole (MBO) and/orbenzotriazole (BTA). The addition of the corrosion inhibitor compoundcan increase the corrosion resistance of the coating so that itsatisfies the requirements of MIL-DTL-81706B Class 1A and Class 3 or theless stringent requirements of MIL-DTL-5541F Class 1A and Class 3.

It should be appreciated that although the corrosion inhibitor additiveserves to substantially increase the coating's corrosion resistance, thecoating can also satisfy the MIL corrosion resistance requirements evenin the absence of such an additive.

The trivalent chromium conversion coating solution can also includeother materials such as thickeners, surfactants, and the like. Examplesof these materials can be found in the patents incorporated by referenceat the end of the description. These materials can be included in thetrivalent chromium conversion coating solution in any of the quantitiesdisclosed in the patents.

Conversion Coating Solution Formation

The trivalent chromium conversion coating solution can take a variety offorms. In some embodiments, the conversion coating solution is the finalmixed solution having the concentrations of the various compoundsdescribed above. In other embodiments, the trivalent chromium conversioncoating solution is a concentrate containing all of the variouscompounds in the final mixed solution including the dye. In theseembodiments, the dye and other compounds are included in the concentratein a concentrated amount sufficient to produce the concentrationsdescribed above when diluted appropriately. The final mixed solution isformed by diluting the concentrate with water at a ratio ofapproximately 1:1.5 to approximately 1:8, respectively, or at a ratio ofapproximately 1:2 to approximately 1:5, respectively.

In yet other embodiments, the trivalent chromium conversion coatingsolution can be formed by mixing a dye additive with a conversioncoating concentrate or diluted solution (solution diluted to the levelsof the final mixed solution but without a dye). In these embodiments,the dye additive can be a separate product that is separately packagedand sold for use with standard conversion coating solutions. Forexample, the dye additive can be mixed with standard conversion coatingsolutions such as CHEMEON TCP-HF (trivalent chromium post treatmentcomposition that does not include a phosphorous compound) and CHEMEONTCP-NP (trivalent chromium post treatment composition that includes aphosphorous compound), both of which are available from CHEMEON SurfaceTechnology, Minden, Nev. The dye additive can be used to change thecolor of the conversion coating solution and, subsequently, the coatedsubstrate.

This gives the end user a great deal of flexibility in terms of decidingwhether or not to add a dye to the conversion coating solution. If theuser wants to add a dye to change the color of the substrate, then theuser can add the additive to the conversion coating solution beforeapplying it to the substrate. On the other hand, if the user does notwant to add a dye then the user can just use the conversion coatingsolution as is.

The dye additive can take a number of forms and include a variety ofdifferent compounds. The dye additive is preferably an aqueous solutioncomprising the dye compound. It can include any of the dye compoundsdescribed above. When used, the dye additive is typically the onlysource of dye for the trivalent chromium conversion coating solution. Inother words, the solution to which the dye additive is added preferablydoes not already contain any dye.

The dye additive can also include other compounds. In some embodiments,the dye additive includes one or more of the corrosion inhibitorcompounds described above. In other embodiments, the dye additiveincludes one or more of the trivalent chromium compounds describedabove. In yet other embodiments, the dye additive includes bothcorrosion inhibitor compounds and trivalent chromium compounds.

If the dye additive only includes the dye compound, then adding it tothe conversion coating solution further dilutes the other compounds inthe solution. This isn't a problem provided that the additional dilutionprovided the dye additive is accounted for. On the other hand, if thedye additive includes proportional amounts of the other compounds in theconversion coating solution, then adding it won't affect theconcentration of those compounds.

For example, the conversion coating concentrate may instruct the user todilute it with water at a ratio of 1:4 to form the final mixed solution.If the user follows the instructions and then adds the dye additivecontaining only the dye compound, it will further dilute the solutionbeyond the desired level. However, if the dye additive containsproportional amounts of the other compounds in the conversion coatingconcentrate, then the user can add it to the final mixed solutionwithout changing the concentration of the various compounds. In general,this is the preferred method because it is easier for users tounderstand and apply.

The concentration of each compound in the dye additive is such that whenit is combined with the conversion coating solution it produces a finalmixed solution where each compound has the concentration describedabove. Accordingly, if the dye additive is diluted by a factor of fourto form the final mixed solution, then the concentration of the variouscompounds in the dye additive are four times the amount described above.Thus, the dye additive is also a concentrate of those compounds itcontains.

The dye additive can be diluted any suitable amount to form the finalmixed solution. In some embodiments, the dye additive is diluted at aratio of approximately 1:1.5 to approximately 1:8 or at a ratio ofapproximately 1:2 to approximately 1:5. The dye additive can be dilutedby mixing it with the conversion coating solution in the form of aconcentrate or a diluted solution (diluted to the level of the finalmixture). If the dye additive is mixed with the conversion coatingsolution concentrate, then it can be further diluted with water prior touse.

A typical example of a final mixed solution includes one part trivalentchromium conversion coating solution concentrate, one part dye additive,and two parts water. The final mixed solution can be sold as an alreadymixed ready to use product or as separate components—i.e., theconversion coating solution concentrate and dye additive—that the usermixes together and dilutes with water.

The trivalent chromium conversion coating solution is an acidic aqueoussolution that can have any suitable pH. During storage, the pH of thetrivalent chromium conversion coating solution can vary substantially.For example, during storage, the pH can vary from approximately 1.0 toapproximately 4.5. When the trivalent chromium conversion coatingsolution is used to treat a metal substrate, the pH should be adjustedto be approximately 2.5 to approximately 4.5 or, preferably,approximately 3.5 to approximately 4.

The trivalent chromium conversion coating solution can be used to treatany suitable metal substrate. In some embodiments, the trivalentchromium conversion coating solution can be used to treat substratescomprising aluminum, magnesium, and/or zinc. The substrates can be pureor commercially pure aluminum, magnesium, or zinc. The substrates canalso be an alloy of these metals or an alloy that includes these metals.

In other embodiments, the conversion coating solution can be used totreat substrates comprising valve metals such as vanadium, tantalum,hafnium, niobium, and/or tungsten. The substrates can be a pure orcommercially pure elemental valve metal. The substrates can also be analloy of a valve metal or an alloy that includes a valve metal.

The metal substrate can be subjected to another treatment prior to beingtreated with the conversion coating solution. For example, the metalsubstrate can be anodized before being treated with the conversioncoating solution.

The metal substrate can take a variety of forms. In some embodiments,the metal substrate is one or more surfaces of a larger metal part orassembly. For example, the metal substrate may be an exposed metalsurface of an aircraft. In other embodiments, the metal substrate is asingle part that can be made from a monolithic block of metal or fromcoupling multiple metal components together.

A variety of methods can be used to treat the metal substrate with theconversion coating solution. In general, the method can comprise one ormore of the steps of: (a) cleaning the metal substrate, (b) rinsing thecleaner off the metal substrate, (c) activating the metal substratesusing an activator solution, (d) rinsing the activator solution off themetal substrate, (e) applying the trivalent chromium conversion coatingsolution to the metal substrate (e.g., immersion, spray, brush, wipe,and/or the like), (f) rinsing the conversion coating solution off themetal substrate, and (g) drying the metal substrate (either actively orpassively). Also, the methods can be the same or similar to the methodsused to treat metal substrates with non-colorized conversion coatingsolutions such as CHEMEON TCP-HF and CHEMEON TCP-NP.

It should be noted that because the dye is an integral part of thetrivalent chromium conversion coating solution, the process of coatingand dying the substrate can be performed in a single step. Manyconventional methods for dying a metal substrate are two step processes.The first step in such processes is to apply the conversion coating,typically by immersing the substrate in a bath. The second step in suchprocesses is to apply the dye, also typically done by immersion. Theinstant process can apply the conversion coating and colorsimultaneously.

EXAMPLES

The following examples are provided to further illustrate the disclosedsubject matter. They should not be used to constrict or limit the scopeof the claims in any way.

Example 1

A first sample of a magnesium substrate (AZ31B alloy) was coated with adye containing trivalent chromium zirconate conversion coating solution.A second sample of the same substrate was coated with the sameconversion coating except without the dye. The samples were initiallycleaned by immersing them in CHEMEON Magnesium Cleaner for 5 minutespursuant to the instructions in the technical data sheet (20% v/v, 150°F.). The samples were removed from the cleaner and rinsed by immersingthem in deionized water at room temperature for 30-60 seconds. Thesamples were activated by immersing them in CHEMEON Magnesium Activatorfor 15 minutes pursuant to the instructions in the technical data sheet(25% v/v, pH 4.5, 82° F.).

The samples were removed from the activator and rinsed by immersing themin deionized water at room temperature for 30-60 seconds. The firstsample was immersed in the dye containing trivalent chromium conversioncoating solution for 5 minutes. The dye containing conversion coatingsolution included: (1) an aqueous conversion coating solution of 28 vol% CHEMEON TCP-HF and 72 vol % deionized water (aqueous conversioncoating solution: pH 3.8, 95° F.), plus 0.3 wt % of Black Super dye (mixof chromium complex azo dyes), part number 9243, available from SICTechnologies, Atlanta, Ga. The aqueous conversion coating solution was atrivalent chromium zirconate conversion coating solution having acomposition that fell within the ranges disclosed in the patentsincorporated by reference. The second sample was immersed in the sameconversion coating except without the dye.

The samples were removed from the conversion coating solutions andrinsed by immersing them in deionized water at room temperature for30-60 seconds. The samples were allowed to air dry. The first sample hada steely blue color (approximately 70767f in HTML notation) as shown onthe left side of FIG. 1. The second sample had more of a natural graycolor (approximately bdbebe in HTML notation) as shown on the right sideof FIG. 1.

Example 2

A first sample of a zinc substrate (pure zinc) was coated with a dyecontaining trivalent chromium conversion coating solution. A secondsample of the same substrate was coated with the same conversion coatingexcept without the dye. The samples were initially cleaned by immersingthem in CHEMEON Cleaner 1000 for 5 minutes pursuant to the instructionsin the technical data sheet (45 g/L cleaner, 120° F.). The samples wereremoved from the cleaner and rinsed by immersing them in deionized waterat room temperature for 30-60 seconds. The samples were activated byimmersing them in an acid activation bath (2.5 mL/L concentrated nitricacid) at room temperature for 5 seconds.

The samples were removed from the acid activation bath and rinsed byimmersing them in deionized water at room temperature for 30-60 seconds.The first sample was immersed in the dye containing trivalent chromiumconversion coating solution for 5 minutes. The dye containing conversioncoating solution included: (1) an aqueous conversion coating solution of28 vol % CHEMEON TCP-HF and 72 vol % deionized water (aqueous conversioncoating solution: pH 3.8, 95° F.) and (2) 0.3 wt % of Black Super dye(mix of chromium complex azo dyes), part number 9243, available from SICTechnologies, Atlanta, Ga. The aqueous conversion coating solution was atrivalent chromium zirconate conversion coating solution having acomposition that fell within the ranges disclosed in the patentsincorporated by reference. The second sample was immersed in the sameconversion coating except without the dye.

The samples were removed from the conversion coating solutions andrinsed by immersing them in deionized water at room temperature for30-60 seconds. The samples were allowed to air dry. The first sample hada light blue color (approximately 6f99b2 in HTML notation) as shown onthe left side of FIG. 2. The second sample had more of a gray color(approximately 9d9ea0 in HTML notation) as shown on the right side ofFIG. 2

Example 3

A first sample of an aluminum substrate (6061-T6 sheet) was coated witha dye containing trivalent chromium conversion coating solution. Asecond sample of the same substrate was coated with the same conversioncoating except without the dye. The samples were initially cleaned byimmersing them in CHEMEON Cleaner 1000 for 5 minutes pursuant to theinstructions in the technical data sheet (45 g/L cleaner, 120° F.). Thesamples were removed from the cleaner and rinsed by immersing them indeionized water at room temperature for 30-60 seconds. The samples wereactivated by immersing them in an acid activation bath (50% v/vconcentrated nitric acid) at room temperature for 1 minute.

The samples were removed from the acid activation bath and rinsed byimmersing them in deionized water at room temperature for 30-60 seconds.The first sample was immersed in the dye containing trivalent chromiumconversion coating solution for 5 minutes. The dye containing conversioncoating solution included: (1) an aqueous conversion coating solution of28 vol % CHEMEON TCP-HF and 72 vol % deionized water (aqueous conversioncoating solution: pH 3.8, 95° F.) and (2) 0.3 wt % of Black Super dye(mix of chromium complex azo dyes), part number 9243, available from SICTechnologies, Atlanta, Ga. The aqueous conversion coating solution was atrivalent chromium zirconate conversion coating solution having acomposition that fell within the ranges disclosed in the patentsincorporated by reference. The second sample was immersed in the sameconversion coating except without the dye.

The samples were removed from the conversion coating solutions andrinsed by immersing them in deionized water at room temperature for30-60 seconds. The samples were allowed to air dry. The first sample hada dark blue color (approximately 425969 in HTML notation) as shown onthe right side of FIG. 3. The second sample had a dark gray color(approximately 696e71 in HTML notation) as shown on the left side ofFIG. 3.

Example 4

Samples 1-8 were prepared by coating aluminum substrates using theprocedure described in Example 3 and the dyes shown in Table 1. Theconversion coating solutions included: (1) an aqueous conversion coatingsolution of 28 vol % CHEMEON TCP-HF and 72 vol % deionized water(aqueous conversion coating solution: pH 3.8, 95° F.) and (2) 0.3 wt %of the specified dye. The aqueous conversion coating solution was atrivalent chromium zirconate conversion coating solution having acomposition that fell within the ranges disclosed in the patentsincorporated by reference. Samples C1-C2 were prepared by coatingaluminum substrates using the same procedure and conversion coatingsexcept the dyes were conventional dyes CC-600 and CC-600P.

TABLE 1 Dye Test Results Color Bath Corrosion Sample Dye¹ CompositionIntensity² Stability Resistance 1 Liquid Black Chromium complex azo dyeDark blue Good Good (SIC 9237) Strong (336 hr NSS)⁴ 2 Fiery Red Monoazoand disazo dye Reddish pink Poor NA (SIC 9202) mixture Weak 3 BordeauxRed Chromium complex azo dye Reddish pink Poor NA (SIC 9201) Weak 4Black Super Mix of chromium complex Dark blue Good NA (SIC 9243) azo dyeStrong 5 Super Black BK Chromium complex azo dye Blue — — (SIC 9219)Medium 6 Deep Black MLW Chromium complex azo dye Dark blue Good NA (SIC8521) plus shading components Strong 7 Black CRO Metal free trisazo dyePink Fair — (SIC 9213) Weak 8 Black LM Chromium complex azo dye Darkblue Fair — (SIC 9260) Strong C1 CC-600 Copper phthalocyanine Teal-blueCrashed³ Poor Strong C2 CC-600P Pyrocatechol violet Blue Poor poorStrong ¹SIC = SIC Technologies, Atlanta, GA. ²Intensity scale is strong,medium, weak. ³Dye caused the chromium in precipitate out of the bath.⁴Corrosion resistance to 336 hours salt spray (ASTM B117).

The color intensity, bath stability, and corrosion resistance of thecoated substrates are shown in Table 1. Samples 1-8 produced resultsthat were consistently better than the samples produced using theconventional dyes C1 and C2. The black dyes and the chromium complex azodyes produced especially superior results.

The conventional dyes performed poorly. In Sample C1, the dye evenreacted with the chromium in the batch causing it to precipitate out.The bath would still dye the substrate due to the presence of thezirconate compound, but the corrosion resistance is severely compromiseddue to the removal of the chromium.

Example 5

An aluminum substrate was coated using the procedure described inExample 3 and a dye containing conversion coating solution thatincluded: (1) an aqueous solution of 28 vol % CHEMEON TCP-HF and44.5-44.9 vol % deionized water (aqueous conversion coating solution: pH3.8, 95° F.), (2) 0.1-0.5 vol % trivalent chromium sulfate basic, (3) 27vol % of an aqueous solution of 2-mercaptobenzoxazole (0.4 g/liter of2-mercaptobenzoxazole—CAS 2382-96-9), and (4) 0.3 wt % of Liquid Blackdye. The dye containing conversion coating solution includedapproximately 0.1 g/liter of 2-mercaptobenzoxazole. The conversioncoating had a composition that fell within the ranges disclosed in thepatents incorporated by reference (excluding the 2-mercaptobenzoxazole,which is not disclosed in the incorporated patents).

The corrosion resistance of the coated aluminum substrate was tested,and it satisfied the requirements of MIL-DTL-81706B Class 1A and Class 3and the less stringent requirements of MIL-DTL-5541F Class 1A and Class3.

Illustrative Embodiments

Reference is made in the following to several illustrative embodimentsof the disclosed subject matter. The following embodiments illustrateonly a few selected embodiments that may include one or more of thevarious features, characteristics, and advantages of the disclosedsubject matter. Accordingly, the following embodiments should not beconsidered as being comprehensive of all possible embodiments.

In one embodiment, a trivalent chromium conversion coating solutioncomprises: a trivalent chromium compound; a zirconate compound; and adye compound; wherein the conversion coating solution is an aqueoussolution; and wherein the dye compound comprises an azo dye, a chromiumcomplex dye, an anthraquinoid dye, and/or a methine dye.

In some embodiments, the trivalent chromium compound can comprisetrivalent chromium sulfate. The trivalent chromium conversion coatingsolution can comprise approximately 0.1 g/liter to approximately 20g/liter of the trivalent chromium compound.

In some embodiments, the zirconate compound can comprise an alkali metalhexafluorozirconate compound such as potassium hexafluorozirconateand/or sodium hexafluorozirconate. The trivalent chromium conversioncoating solution can comprise approximately 0.2 g/liter to approximately20 g/liter of the zirconate compound.

In some embodiments, the dye compound can comprise a metal complex azodye. The dye compound can comprise a chromium complex azo dye. The dyecompound can comprise a metal free azo dye. The trivalent chromiumconversion coating solution can comprise approximately 0.01 wt % toapproximately 2.0 wt % of the dye compound.

In some embodiments, the trivalent chromium conversion coating solutioncan comprise a phosphorous compound. The trivalent chromium conversioncoating solution can comprise 5 ppm to 100 ppm of the phosphorouscompound. The trivalent chromium conversion coating solution cancomprise an organic amino-phosphonic acid compound. The trivalentchromium conversion coating solution can comprisenitrilotris(methylene)triphosphonic acid.

In some embodiments, the trivalent chromium conversion coating solutioncan satisfy the requirements of MIL-DTL-81706B Class 1A and Class 3and/or the requirements of MIL-DTL-5541F Class 1A and Class 3.

In some embodiments, the trivalent chromium conversion coating solutioncan comprise a corrosion inhibitor compound. The trivalent chromiumconversion coating solution can comprise 2-mercaptobenzothiazole,2-mercaptobenzimidazole, 2-mercaptobenzoxazole, and/or benzotriazole.

In some embodiments, the trivalent chromium conversion coating solutioncan have a pH of approximately 2.5 to approximately 4.5, preferablyapproximately 3.5 to approximately 4. The trivalent chromium conversioncoating solution can comprise: approximately 0.2 g/liter toapproximately 10 g/liter of the trivalent chromium compound;approximately 0.5 g/liter to approximately 18 g/liter of a zirconatecompound; and a pH of approximately 3.5 to approximately 4.

In some embodiments, a method comprises treating a metal substrate withthe conversion coating solution. The metal substrate can comprisealuminum, magnesium, and/or zinc.

In another embodiment, a trivalent chromium conversion coating solutioncomprises: a trivalent chromium sulfate; an alkali metalhexafluorozirconate compound; and a dye compound; wherein the conversioncoating solution is an aqueous solution; and wherein the dye compoundcomprises an azo dye, an anthraquinoid dye, and/or a methine dye.

In some embodiments, the trivalent chromium conversion coating solutioncan comprise: approximately 0.1 g/liter to approximately 20 g/liter ofthe trivalent chromium sulfate; approximately 0.2 g/liter toapproximately 20 g/liter of the alkali metal hexafluorozirconatecompound; and a pH of approximately 2.5 to approximately 4.5. Thetrivalent chromium conversion coating solution can comprise:approximately 0.2 g/liter to approximately 10 g/liter of the trivalentchromium sulfate; approximately 0.5 g/liter to approximately 18 g/literof the alkali metal hexafluorozirconate compound; and a pH ofapproximately 3.5 to approximately 4.

In some embodiments, the dye compound can comprise a metal complex azodye, a chromium complex azo dye, a metal free azo dye. The trivalentchromium conversion coating solution can comprise approximately 0.01 wt% to approximately 2.0 wt % of the dye compound.

In another embodiment, a dye additive for a trivalent chromiumconversion coating solution, the dye additive comprises: water; and adye compound comprising an azo dye, a chromium complex dye, ananthraquinoid dye, and/or a methine dye; wherein the dye additive is anaqueous solution.

In some embodiments, the dye additive can comprise a trivalent chromiumcompound, a corrosion inhibitor compound, and/or a corrosion inhibitor.The corrosion inhibitor can comprise 2-mercaptobenzothiazole,2-mercaptobenzimidazole, 2-mercaptobenzoxazole, and/or benzotriazole.

In some embodiments, a method comprises: mixing a dye additive with atrivalent chromium conversion coating solution to form a mixed solution;wherein the dye additive comprises a dye compound in an aqueoussolution; and wherein the trivalent chromium conversion coating solutioncomprises a trivalent chromium compound and a zirconate compound.

In some embodiments, the method comprises mixing the dye additive andthe trivalent chromium conversion coating solution at a ratio of1:1.5-1:8, respectively, or, preferably, 1:2-1:5, respectively. The dyecompound can comprise an azo dye, a chromium complex dye, ananthraquinoid dye, and/or a methine dye. The dye additive can comprise atrivalent chromium compound. The dye additive can comprise a corrosioninhibitor compound. The dye additive can comprise a trivalent chromiumcompound and a corrosion inhibitor compound. The corrosion inhibitor cancomprise 2-mercaptobenzothiazole, 2-mercaptobenzimidazole,2-mercaptobenzoxazole, and/or benzotriazole.

In some embodiments, the trivalent chromium compound comprises trivalentchromium sulfate. The mixed solution can comprise approximately 0.1g/liter to approximately 20 g/liter of the trivalent chromium compound.The zirconate compound can comprise an alkali metal hexafluorozirconatecompound. The mixed solution can comprise approximately 0.2 g/liter toapproximately 20 g/liter of the zirconate compound. The mixed solutioncan comprise approximately 0.01 wt % to approximately 2.0 wt % of thedye compound. The mixed solution can comprise a phosphorous compound.The mixed solution can have a pH of approximately 2.5 to approximately4.5.

In some embodiments, the mixed solution comprises: approximately 0.2g/liter to approximately 10 g/liter of the trivalent chromium compound;approximately 0.5 g/liter to approximately 18 g/liter of a zirconatecompound; and a pH of approximately 3.5 to approximately 4.

In some embodiments, the method can comprise coating a metal substratewith the mixed solution. The metal substrate can comprise aluminum,magnesium, and/or zinc.

Terminology and Interpretative Conventions

Any methods described in the claims or specification should not beinterpreted to require the steps to be performed in a specific orderunless stated otherwise. Also, the methods should be interpreted toprovide support to perform the recited steps in any order unless statedotherwise.

Spatial or directional terms, such as “left,” “right,” “front,” “back,”and the like, relate to the subject matter as it is shown in thedrawings. However, it is to be understood that the described subjectmatter may assume various alternative orientations and, accordingly,such terms are not to be considered as limiting.

Articles such as “the,” “a,” and “an” can connote the singular orplural. Also, the word “or” when used without a preceding “either” (orother similar language indicating that “or” is unequivocally meant to beexclusive—e.g., only one of x or y, etc.) shall be interpreted to beinclusive (e.g., “x or y” means one or both x or y).

The term “and/or” shall also be interpreted to be inclusive (e.g., “xand/or y” means one or both x or y). In situations where “and/or” or“or” are used as a conjunction for a group of three or more items, thegroup should be interpreted to include one item alone, all the itemstogether, or any combination or number of the items.

The terms have, having, include, and including should be interpreted tobe synonymous with the terms comprise and comprising. The use of theseterms should also be understood as disclosing and providing support fornarrower alternative embodiments where these terms are replaced by“consisting” or “consisting essentially of.”

Unless otherwise indicated, all numbers or expressions, such as thoseexpressing dimensions, physical characteristics, and the like, used inthe specification (other than the claims) are understood to be modifiedin all instances by the term “approximately.” At the very least, and notas an attempt to limit the application of the doctrine of equivalents tothe claims, each numerical parameter recited in the specification orclaims which is modified by the term “approximately” should be construedin light of the number of recited significant digits and by applyingordinary rounding techniques.

All disclosed ranges are to be understood to encompass and providesupport for claims that recite any and all subranges or any and allindividual values subsumed by each range. For example, a stated range of1 to 10 should be considered to include and provide support for claimsthat recite any and all subranges or individual values that are betweenand/or inclusive of the minimum value of 1 and the maximum value of 10;that is, all subranges beginning with a minimum value of 1 or more andending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to3.56, and so forth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994,and so forth).

All disclosed numerical values are to be understood as being variablefrom 0-100% in either direction and thus provide support for claims thatrecite such values or any and all ranges or subranges that can be formedby such values. For example, a stated numerical value of 8 should beunderstood to vary from 0 to 16 (100% in either direction) and providesupport for claims that recite the range itself (e.g., 0 to 16), anysubrange within the range (e.g., 2 to 12.5) or any individual valuewithin that range (e.g., 15.2).

The terms recited in the claims should be given their ordinary andcustomary meaning as determined by reference to relevant entries inwidely used general dictionaries and/or relevant technical dictionaries,commonly understood meanings by those in the art, etc., with theunderstanding that the broadest meaning imparted by any one orcombination of these sources should be given to the claim terms (e.g.,two or more relevant dictionary entries should be combined to providethe broadest meaning of the combination of entries, etc.) subject onlyto the following exceptions: (a) if a term is used in a manner that ismore expansive than its ordinary and customary meaning, the term shouldbe given its ordinary and customary meaning plus the additionalexpansive meaning, or (b) if a term has been explicitly defined to havea different meaning by reciting the term followed by the phrase “as usedin this document shall mean” or similar language (e.g., “this termmeans,” “this term is defined as,” “for the purposes of this disclosurethis term shall mean,” etc.). References to specific examples, use of“i.e.,” use of the word “invention,” etc., are not meant to invokeexception (b) or otherwise restrict the scope of the recited claimterms. Other than situations where exception (b) applies, nothingcontained in this document should be considered a disclaimer ordisavowal of claim scope.

The subject matter recited in the claims is not coextensive with andshould not be interpreted to be coextensive with any embodiment,feature, or combination of features described or illustrated in thisdocument. This is true even if only a single embodiment of the featureor combination of features is illustrated and described in thisdocument.

Incorporation by Reference

The entire content of each of the documents listed below areincorporated by reference into this document. If the same term is usedin both this document and one or more of the incorporated documents,then it should be interpreted to have the broadest meaning imparted byany one or combination of these sources unless the term has beenexplicitly defined to have a different meaning in this document. Ifthere is an inconsistency between any of the following documents andthis document, then this document shall govern. The incorporated subjectmatter should not be used to limit or narrow the scope of the explicitlyrecited or depicted subject matter.

-   -   U.S. Prov. App. No. 62/453,495, titled “Dyed Non-Hexavalent        Chromium Conversion Coating,” filed on 1 Feb. 2017.    -   U.S. Prov. App. No. 62/588,129, titled “Dyed Trivalent Chromium        Conversion Coatings,” filed on 17 Nov. 2017.    -   U.S. Pat. No. 6,375,726 (application Ser. No. 09/702,225),        titled “Corrosion Resistant Coatings for Aluminum and Aluminum        Alloys,” filed on 31 Oct. 2000, issued on 23 Apr. 2002.    -   U.S. Pat. No. 6,511,532 (application Ser. No. 10/012,982),        titled “Post-Treatment for Anodized Aluminum,” filed on 6 Nov.        2001, issued on 28 Jan. 2003.    -   U.S. Pat. No. 6,521,029 (application Ser. No. 10/116,844),        titled “Pretreatment for Aluminum and Aluminum Alloys,” filed on        5 Apr. 2002, issued on 18 Feb. 2003.    -   U.S. Pat. No. 6,527,841 (application Ser. No. 10/012,981),        titled “Post-Treatment for Metal Coated Substrates,” filed on 6        Nov. 2001, issued on 4 Mar. 2003.    -   U.S. Pat. No. 6,669,764 (application Ser. No. 10/351,752),        titled “Pretreatment for Aluminum and Aluminum Alloys,” filed on        23 Jan. 2003, issued on 30 Dec. 2003.    -   U.S. Pat. No. 7,018,486 (application Ser. No. 10/187,179),        titled “Corrosion Resistant Trivalent Chromium Phosphated        Chemical Conversion Coatings,” filed on 27 Jun. 2002, issued on        28 Mar. 2006.    -   The portions of CN 102888138A, titled “Low-temperature        anti-corrosion protective agent for surfaces of automobile        parts,” disclosing and describing corrosion inhibitor compounds.

1. A trivalent chromium conversion coating solution comprising: atrivalent chromium compound; a zirconate compound; and a dye compound;wherein the conversion coating solution is an aqueous solution; andwherein the dye compound comprises an azo dye, a chromium complex dye,an anthraquinoid dye, and/or a methine dye.
 2. The trivalent chromiumconversion coating solution of claim 1 wherein the trivalent chromiumcompound comprises trivalent chromium sulfate.
 3. The trivalent chromiumconversion coating solution of claim 1 comprising approximately 0.1g/liter to approximately 20 g/liter of the trivalent chromium compound.4. The trivalent chromium conversion coating solution of claim 1 whereinthe zirconate compound comprises an alkali metal hexafluorozirconatecompound.
 5. The trivalent chromium conversion coating solution of claim1 comprising approximately 0.2 g/liter to approximately 20 g/liter ofthe zirconate compound.
 6. The trivalent chromium conversion coatingsolution of claim 1 wherein the dye compound comprises a metal complexazo dye.
 7. The trivalent chromium conversion coating solution of claim1 wherein the dye compound comprises a chromium complex azo dye.
 8. Thetrivalent chromium conversion coating solution of claim 1 wherein thedye compound comprises a metal free azo dye.
 9. The trivalent chromiumconversion coating solution of claim 1 comprising approximately 0.01 wt% to approximately 2.0 wt % of the dye compound.
 10. The trivalentchromium conversion coating solution of claim 1 comprising a phosphorouscompound.
 11. The trivalent chromium conversion coating solution ofclaim 1 wherein the trivalent chromium conversion coating satisfies therequirements of MIL-DTL-81706B Class 1A and Class 3 and/or MIL-DTL-5541FClass 1A and Class
 3. 12. The trivalent chromium conversion coatingsolution of claim 1 comprising 2-mercaptobenzothiazole,2-mercaptobenzimidazole, 2-mercaptobenzoxazole, and/or benzotriazole.13. The trivalent chromium conversion coating solution of claim 1wherein the trivalent chromium conversion coating solution has a pH ofapproximately 2.5 to approximately 4.5.
 14. A method comprising treatinga metal substrate with the conversion coating solution of claim 1,wherein the metal substrate comprises aluminum, magnesium, and/or zinc.15. A trivalent chromium conversion coating solution comprising: atrivalent chromium sulfate; an alkali metal hexafluorozirconatecompound; and a dye compound; wherein the conversion coating solution isan aqueous solution; and wherein the dye compound comprises an azo dye,an anthraquinoid dye, and/or a methine dye.
 16. The trivalent chromiumconversion coating solution of claim 15 comprising: approximately 0.1g/liter to approximately 20 g/liter of the trivalent chromium sulfate;approximately 0.2 g/liter to approximately 20 g/liter of the alkalimetal hexafluorozirconate compound; and a pH of approximately 2.5 toapproximately 4.5.
 17. The trivalent chromium conversion coatingsolution of claim 15 comprising: approximately 0.2 g/liter toapproximately 10 g/liter of the trivalent chromium sulfate;approximately 0.5 g/liter to approximately 18 g/liter of the alkalimetal hexafluorozirconate compound; and a pH of approximately 3.5 toapproximately
 4. 18. The trivalent chromium conversion coating solutionof claim 15 wherein the dye compound comprises a metal complex azo dye.19. The trivalent chromium conversion coating solution of claim 15wherein the dye compound comprises a chromium complex azo dye.
 20. Thetrivalent chromium conversion coating solution of claim 15 wherein thedye compound comprises a metal free azo dye.
 21. The trivalent chromiumconversion coating solution of claim 15 comprising approximately 0.01 wt% to approximately 2.0 wt % of the dye compound.
 22. The trivalentchromium conversion coating solution of claim 15 comprising an organicamino-phosphonic acid compound.
 23. The trivalent chromium conversioncoating solution of claim 15 comprising 2-mercaptobenzothiazole,2-mercaptobenzimidazole, 2-mercaptobenzoxazole, and/or benzotriazole.24. A dye additive for a trivalent chromium conversion coating solution,the dye additive comprising: water; and a dye compound comprising an azodye, a chromium complex dye, an anthraquinoid dye, and/or a methine dye;wherein the dye additive is an aqueous solution.
 25. The dye additive ofclaim 24 comprising a trivalent chromium compound.
 26. The dye additiveof claim 24 comprising a corrosion inhibitor compound.
 27. The dyeadditive of claim 24 comprising a trivalent chromium compound and acorrosion inhibitor.
 28. The dye additive of claim 27 wherein thecorrosion inhibitor comprises 2-mercaptobenzothiazole,2-mercaptobenzimidazole, 2-mercaptobenzoxazole, and/or benzotriazole.29. A method comprising: mixing a dye additive with a trivalent chromiumconversion coating solution to form a mixed solution; wherein the dyeadditive comprises a dye compound in an aqueous solution; and whereinthe trivalent chromium conversion coating solution comprises a trivalentchromium compound and a zirconate compound.
 30. The method of claim 29wherein the dye compound comprises an azo dye, a chromium complex dye,an anthraquinoid dye, and/or a methine dye.